Hullo,
As our 5 chickens dwindled to two we found that one would lay under some ivy on the garden wall and the other in an unknown location despite over a year of being good chickens and laying in the house.
The fox finally took us down to one solitary chicken (who was laying under the ivy), our neighbours cut the ivy down, from their side of the wall exposing her laying place. After that she went back to laying in the house which was a big surprise.
I don't supose you want to go to the lenghts of cutting down your bush but maybe chicken wiring it in for a week will get her out of the habit, or may make her lay somewhere else you don't know about!
Sarah